Carbonylation of an alcohol and/or reactive derivative thereof to produce a carboxylic acid and/or carboxylic acid anhydride is known, as described for example in EP-A-0 144 935, EP-A-0 643 034 and U.S. Pat. No. 6,211,405.
A typical homogeneously catalysed carbonylation process entails contacting carbon monoxide with a liquid reaction composition comprising an alcohol and/or reactive derivative thereof and a group VIII carbonylation catalyst (typically rhodium and/or iridium) in a reaction zone at elevated temperature and pressure, optionally in the presence of one or more co-catalysts and/or promoters. Carboxylic acid and/or carboxylic acid anhydride is recovered from the liquid reaction composition by feeding the liquid reaction composition to a flash separation zone, wherein a liquid fraction comprising the carbonylation catalyst is returned to the reaction zone, and a vapour fraction comprising carboxylic acid and/or carboxylic acid anhydride, is fed to one or more distillation columns to separate unreacted reactants and by-products from the desired carboxylic acid and/or carboxylic acid anhydride product.
However, a problem associated with carbonylation processes is that heat can be lost from process streams whose temperature is too low to be readily and economically used elsewhere, for example whose temperature is insufficient to be transferred to a supply of pressurised steam. Such process streams are often cooled by a supply of cooling water before being sent to storage or transportation means, and so the heat is lost as waste as opposed to being captured and usefully employed.
In U.S. Pat. No. 6,114,576, an exothermic, heterogeneously catalysed carbonylation process is described in which heat from a stream withdrawn from the reactor is captured by heating process streams in the product recovery section of the process. Additionally, GB 1,261,170 describes a heat management process in the production of urea, in which heat released by condensation in a recycle stream is transferred to a reactant stream.
However, there remains a need for a carbonylation process in which heat that is otherwise lost as waste can be captured and usefully employed elsewhere, either in the same carbonylation process or in a different process.